A new opinion piece co-authored by George Conway III - husband of White House counselor Kellyanne Conway - argues that President Donald Trump's installation of Matthew Whitaker as acting attorney general Wednesday was unconstitutional.

"It's illegal. And it means that anything Mr. Whitaker does, or tries to do, in that position is invalid," George Conway wrote with his co-author in a piece published by the New York Times on Thursday, less than 24 hours after Trump ousted Jeff Sessions from the post.

George Conway's piece was his latest in a series of public shots at the policies of his wife's boss. Just last week, Conway, a lawyer, took aim at Trump's pledge to end birthright citizenship in another op-ed, calling that plan unconstitutional, as well.

Once again, the Conways were on opposite sides of a policy fight Thursday. Earlier in the day, Kellyanne Conway defended Trump's actions to reporters outside the White House.

She dismissed Democrats who have suggested that the replacement of Sessions could lead to a constitutional crisis, particularly if Whitaker moves to shut down the probe by special counsel Robert Mueller into Russia election interference.

"Well, the Democrats don't seem to begin or end a sentence these days without having the word 'crisis' in it," Kellyanne Conway said. "There's not a constitutional crisis."

She added that the White House has "been very compliant with the Mueller investigation."

In his piece, George Conway argued that Whitaker should to be subject to Senate confirmation before serving. Because he wasn't, "there has been no mechanism for scrutinizing whether he has the character and ability to evenhandedly enforce the law in such a position of grave responsibility," the piece said. "The public is entitled to that assurance, especially since Mr. Whitaker's only supervisor is President Trump himself, and the president is hopelessly compromised by the Mueller investigation."

The piece is co-authored with Neal Katyal, who was an acting solicitor general under President Barack Obama.

The two lawyers pull no punches in offering their assessment of Trump's latest controversial move.

"For the president to install Mr. Whitaker as our chief law enforcement officer is to betray the entire structure of our charter document," they wrote.